It is known to produce hollow flange members by cold forming light gauge steel strip to form a section having a planar web and hollow triangular cross-section flanges extending along opposite sides of the web. U.S. Pat. Nos. 991,603 and 3,342,007 describe the manufacture of such beams by a cold forming process wherein the free edge of the hollow flange lies adjacent the edge of the web but is not secured thereto. These hollow flanges are known as “open” flanges and lack torsional resistance.
U.S. Pat. No. 3,698,224 describes the manufacture of hollow flange beams by a cold forming process wherein seam welded steel tubing is subjected to a shaping process which flattens the tube to form a hollow flange beam with a pair of juxtaposed webs.
In order to improve the section efficiency of “open” flange beams, it has been proposed to secure the edges of the hollow flanges to the web to improve torsional stiffness in the flanges. U.S. Pat. Nos. 6,436,552, 6,115,986, 6,397,550 and 5,692,353 describe cold formed thin gauge hollow flange beams wherein a lip formed along the edge of the hollow flange is secured to the web intermediate its edges by fasteners, clinch perforations, spot welding or the like.
Russian Inventor's Certificate 827723 describes a cold formed thin gauge hollow flange beam wherein the free edges of the hollow flanges are formed as internally folded lips or formations to support the hollow flanges against localized crushing under load. A side wall of the hollow flange is welded by a fillet weld to the edge of the web to form a “closed” flange.
In order to reduce the costs of manufacture of cold formed “closed” hollow flange beams, an in-line dual welding process was devised and described in U.S. Pat. No. 5,163,225, in respect of which, the assignee of the present invention is the successor in title. The dual welding process described for the first time an in-line high frequency induction or resistance welding process wherein a free edge of a hollow flange was welded to the face of the strip of metal to form a weld seam adjacent the edge of the web of the hollow flange beam so formed. In that process, a conventional tube rolling mill was adapted to produce hollow flange beams having circular cross-section flanges at the weld station, the circular cross-section flanges subsequently being shaped to triangular cross-section to form “Dogbone” (Registered Trade Mark) beams.
While generally satisfactory for a relatively narrow range of web and flange widths and a narrow range of metal strip gauges, an adaptation to a conventional mill structure was considered to be not only limiting in the scope of beam sizes but also inefficient and capital intensive in terms of requiring a large number of roll sets of large diameter which caused considerable unproductive downtime each time a roll change was required for a different beam size. Moreover, difficulties in maintaining weld seam stability imposed severe limitations on yield due to a high reject rate.
One proposal to address some of the shortcomings in the original “Dogbone” process was described in U.S. Pat. No. 5,403,986. This document proposed a tandem mill structure with separate spaced cold forming mills inclined to a longitudinal axis in a forming section of the mill. Shaped flanges, independently produced from separate strips of metal were brought together with a third planar web strip such that the edges of the web protruded between the free edges of the flanges prior to welding. The welding and forming stations were substantially the same as those described in U.S. Pat. No. 5,163,225.
As used herein, the expression “ERW” refers to electrical resistance or induction welding using either contacts or induction coils/impeders to create a current in the member and other forms of electrical resistance welding.
It is an aim of the present invention to overcome or alleviate at least some of the disadvantages of prior art methods and apparatus for the production of hollow flange seam welded beams.